In order to be able to program cardiac pacemakers on an individual patient basis and thus to be able to provide each patient with therapies which are matched to the cardiac disease of the patient, cardiac pacemakers (CPM) nowadays have a multiplicity of parameters, by means of which the mode of operation of the pacemaker and therewith the therapy afforded by the pacemaker in operation can be adjusted.
Those parameters are programmed for the first time on an individual patient basis in the implantation procedure. Thereafter at regular intervals (typically every 6 months) the patient comes for so-called post-care investigation in which not only the battery and the set pacing and sensing thresholds are checked but in some circumstances also parameters in regard to altered symptoms are re-adjusted.
That procedure admittedly makes it possible to program patient-specific therapies, but they are fixedly set for the following period of time, up to the next post-care investigation. For that reason, the manufacturers of cardiac pacemakers have already long been endeavoring to continuously automatically adapt the parameters to the current requirements of a patient.
Many rate-adaptive cardiac pacemakers are known, in which a large number of physiological parameters are detected as indicators of the metabolic demand and used to control rate adaptation.
DE 199 40 952 discloses a rate-adaptive cardiac pacemaker in which rate adaptation is effected in dependence on the respiration rate. In that respect the basic starting point involved is the central-nervous coupling of respiration and circulatory activity, in which in particular heart rate, heart beat volume and vasomotor system are of significance as circulation-relevant parameters. Measurement of the respiration rate can be effected by measurements in respect of the intrathoracal and/or intracardial impedance.
EP 0 449 401 also discloses a rate-adaptive cardiac pacemaker which has an impedance system for measuring a right-ventricular (or atrial) volume or a pressure transducer for measuring the right-ventricular (or atrial) pressure and a signal processing unit for beat-wise (“beat-to-beat”) extraction of one of the volume or pressure parameters in order thereby to obtain a signal which varies with the respiration rate, and has a peak-to-peak amplitude proportional to the depth of respiration. In that arrangement the signal processing unit is provided to extract the period of the respiration signal and to use the peak-to-peak amplitude and the resulting signals to determine the required stimulation rate for the cardiac pacemaker.
Algorithms for stabilization of the cardiac frequency are known for example from PACE, Vol. 23, October 2000, Part I, pages 1509 ff.